I. Field of the Invention
The present invention relates to an improved cutting machine assembly for cutting a workpiece made of styrofoam or similar material.
II. Description of the Prior Art
Forms made of styrofoam or similar material are frequently used in casting operations. Such forms are typically cut in the shape of the desired casting and the mold material, known as green sand, is applied to the outside of the styrofoam form. The styrofoam form is then liquefied by heating and removed by pouring from the resulting sand mold. After its removal, the sand mold is filled with the molten metal in the conventional fashion thus forming the casting.
It has been the previous practice to construct the styrofoam forms by hand cutting the styrofoam from styrofoam blocks. For large castings, multiple blocks are individually cut and the resulting forms are then laminated together to form the final styrofoam form.
The previously known method of hand cutting the styrofoam to the desired shape, however, suffers from a number of disadvantages. One disadvantage is that, as in all hand operations, it is virtually impossible to obtain high accuracy of the final styrofoam form. Such inaccuracies in the cutting of the styrofoam form by hand may require additional machining of the final casting.
A still further disadvantage of cutting the styrofoam form by hand is that measuring and layout errors can and do occur. Depending upon the magnitude of such errors, destruction of the styrofoam form may be necessary.
A still further disadvantage of hand cutting styrofoam forms is that the hand tools used to cut the styrofoam forms can only attain a rough cut of the styrofoam. This rough cut results from the cellular or bead nature of the styrofoam so that, when hand cutting occurs, the beads or cells of the styrofoam pull away from the styrofoam block and leave a rough surface. Such a rough surface will cause a corresponding rough surface on the sand mold and a like rough surface on the finished casting. Such rough surfaces disadvantageously increase the amount of machining required for the final cast part.
In order to overcome these previously known disadvantages of hand cutting the styrofoam forms, there have been previously known gantry systems, such as disclosed in my prior U.S. Pat. Nos. 5,429,460 and 5,487,630 in which the styrofoam block is mounted on a stationary planar base. A rotary cutter is then mounted to the gantry above the base and this cutter is movable in all three Cartesian coordinates. A computer system controls the actual movement of the cutter which provides high accuracy and repeatability.
My previous gantry systems of the type disclosed in my patents utilize an elongated cylindrical cutter having an axial throughbore. A plurality of radial pores extended through the cutter and intersect the axial bore to thus establish fluid communication from outside the cutting tool and to the axial bore of the cutting tool.
An air vacuum source was then fluidly connected to the inner axial end of the cutting tool axial bore so that, upon actuation, the vacuum source inducted air and styrofoam debris radially inwardly through the cutting tool radial pores, into the axial passageway of the cutting tool and ultimately to a debris collection area for the vacuum source.
There are, however, two disadvantages of my previously known gantry systems. One disadvantage was that, in certain situations, only a very small diameter cutting tool could be mounted to the gantry motor. In these situations, an axially extending passageway could not be provided through the cutting tool due to its small size. Consequently, when these situations were presented, the removal of the styrofoam debris by the vacuum source could not be achieved.
My previously known gantry system utilized a motor with a tubular motor shaft rotatably secured to the motor housing by spaced bearing assemblies. The cutting tool was secured to an outer or lower end of the drive shaft so that the axial bore of the cutting tool, if present, fluidly communicated with the interior of the motor shaft. The vacuum source was then connected to the end of the motor shaft opposite from the cutting tool so that air inducted by the vacuum source through the cutting tool also passed through the motor shaft and cooled the motor windings.
In some situations, however, the air flow through the motor shaft was either low or nonexistent such that the motor shaft as well as the motor housing around the motor shaft became excessively heated by the motor windings. This heating of the motor housing together with the motor shaft, in turn, caused thermal growth of the motor shaft and the motor housing.
Since the motor housing was secured to the gantry only at its end opposite from the cutting tool, the thermal expansion or thermal growth of the motor housing and the motor shaft effectively vertically displaced the cutting tool. When this occurred, dimensional errors were imparted to the styrofoam cut during the cutting operation.